1. Field of the Invention
This invention relates to a paper machine mesh, in particular a forming mesh.
2. Description of the Related Art
Forming meshes are used in the forming section of a paper machine. During the forming process, a fiber suspension from the headbox of the paper machine is applied to one forming mesh or to two forming meshes (in the case of gap formers). The forming mesh in this case dewaters the fiber suspension and forms a fibrous web, wherein as little cellulose fiber and filler material as possible should be separated from the fiber suspension during the dewatering process.
The quality of the formed fibrous web is co-defined in this case to a great extent by the structure of the surface of the forming mesh facing the fibrous web (paper side). The life of the forming mesh, on the other hand, is greatly influenced by the structure of the surface of the forming mesh facing the paper machine (machine side).
To be able to take account of these in part contradictory requirements, multilayer paper machine meshes with a paper-side fabric layer and a machine-side fabric layer were developed, wherein the two fabric layers are connected to each other by so-called ties. To guarantee as uniform a paper-side fabric structure as possible, the tie threads are an integral component of the paper-side weaving structure (integral tie threads), as the result of which a tendency to marking due to the tying of the tie threads is reduced.
Multilayer forming meshes are known from EP 0 432 413, DE 297 24 238 U1, EP 1 00 197 B1 and US 2004/0149342 A1 for example.
The multilayer forming meshes known from the prior art often display, in spite of having a paper-side and a machine-side fabric layer, insufficient resistance to wear caused by irregular abrasion of the machine side of the mesh in some regions, in particular when used on high-speed paper machines.
The irregular abrasion is caused inter alia by the poor flatness of the machine side of the known paper machine meshes. In this case the poor flatness is caused inter alia by an irregular distribution of the tie points, meaning the points at which a tie thread runs on the machine side of the lower fabric layer and crosses a thread of the lower fabric layer. Furthermore, the irregular abrasion is caused inter alia by respectively unequal floating lengths between consecutive tie points of at least some floating weft threads on the outer side of the machine-side fabric layer, which, as is known, have the function of protecting the load-bearing warp threads.
In addition, the irregular connection of the two fabric layers often results in insufficient flatness of the paper side, as the result of which the tendency to marking is notably increased in particular for graphic papers.
Furthermore, the forming meshes known from the prior art often display excessive water entrainment caused by too great a thickness of the mesh, in particular when used on high-speed paper machines (machine speeds of 1500 m/min and more).
Too great a thickness of the mesh is often owed to insufficient connection of the paper-side fabric layer to the machine-side fabric layer by the tie threads.
An insufficient connection between the paper-side fabric layer and the machine-side fabric layer leads moreover, during operation of the paper machine mesh on the paper machine, to a relative movement between the two fabric layers, thus resulting in abrasion between said layers, which can lead to the failure of such meshes.
What is needed in the art is a paper machine mesh on which the connection between the paper-side and machine-side fabric layers is improved and the above described disadvantages are at least reduced accordingly.